To be honest, coming from someone who got all 3 roles, there are just some fights/dungeons I just don't want to heal (perfect example: Titan). This could be only me though...
Maybe the new tank mount rewards led to a sudden influx of tanks again, outnumbering healers right now.
Aside of that, I think many just don't like playing SCH - and if they don't like WHM either, there's no way to play healer lol - I'd say we need a third healer class from Ul'dah ( roots for Time Mage from THM! :> )